In recent years, silver halide-utilized photographic light-sensitive materials have attained increasing development in their photographic properties. As a result, color images of high quality can be obtained with ease at present. In the system usually referred to as color photography, for instance, photographs are made with color negative films, and the image information recorded on each of the developed color negative films is optically printed on color photographic paper, thereby providing color prints. The latest high degree of development in this process and the spread of not only the so-called color lab as a large-scale local base, wherein color prints are mass-produced at high efficiency, but also the so-called mini-lab, or small-sized simplified print processors installed in stores, have enabled everybody to easily amuse oneself with color photographs.
As the principle of color photography which prevails at the present, the optical print system using color reproduction based on subtractive color process is usually adopted. A general color negative has on a transparent support at least three kinds of light-sensitive layers using silver halide emulsions as light-sensitive elements on which are conferred sensitivities in the blue, green and red regions respectively. And the so-called color couplers forming yellow, magenta and cyan dyes respectively are incorporated into the foregoing light-sensitive layers so that the hue of the dye formed from each color coupler bears the complementary color relation to the color sensitivity of the light-sensitive layer into which the color coupler is incorporated. The color negative films exposed imagewise by photography are developed in a color developer containing an aromatic primary amine developing agent. Therein, the exposed silver halide grains are developed, or reduced, by the developing agent, and at the same time the developing agent is oxidized. The thus oxidized developing agent undergoes the coupling reaction with the color couplers as mentioned above to form dyes. Further, the metallic silver produced by development (developed silver) and silver halide remaining unreacted are removed by bleach processing and fixation processing respectively. Thus, dye images are obtained. The color photographic paper, namely a color photosensitive material comprising a reflective support coated with light-sensitive layers wherein the sensitive wavelength region and the hue of the developed color are combined in the same manner as described above, is subjected to optical exposure via a photographically processed color negative film. Further, the thus exposed color photographic paper is subjected to successive color development, bleach and fixation in the same manners as the above, thereby providing the color print made up of dye images reproducing the original scene.
Besides such a classic image formation method, the formation of prints by converting the image information recorded in color negative to digital information by means of a scanner and then subjecting the digital information to diverse image processing to improve the image quality has become possible lately. Actually, the mini-lab systems loaded with such image processing devices are in operation, too.
Under these circumstances, the demand for enhancing the simplicity and easiness of the method for forming images in color negative is growing. The actual situation in the image formation in color negative has the following three problems: Firstly, the processing baths for color development, bleach and fixation require accurate control of their compositions and temperatures, so that special knowledge and skilled operation are necessitated. Secondly, the processing baths contains ingredients the discharge of which is regulated from the view point of environmental protection, such as color developing agents and chelate compounds having iron ion at the center, which are used as bleaching agent, so that there are not a few cases where facilities for environmental protection are required for the installation of developing apparatus and so on. Thirdly, the processing time, though it has been shortened by the recent technical developments, is not yet short enough to meet the current requirement for rapid reproduction of recorded images.
In such contexts, there is a growing demand for construction of a color image formation system that uses neither color developing solution no bleaching solution, which are used in the existing color image formation system, and thereby enables reduction in a load of environmental pollution and improvement in simplicity and easiness of color image formation. In addition, continued improvement toward limitless simplification of the image formation method using processing solutions is also indispensable in competing against the system using an electronic still camera.
In view of the situation mentioned above, many improved arts have been proposed. For instance, the system disclosed in IS & T's 48th Annual Conference Proceedings, page 180, makes a bleach-fix bath, which is essential to the conventional color photographic processing, unnecessary by transferring the dyes produced by development reaction into a mordant layer and then peeling apart the mordant layer to effect the removal of developed silver and silver halide remaining unreacted. However, the art proposed therein still requires the development using a processing bath containing a color developing agent, and so it is hard to say that the environmental protection problem is solved thereby.
As to the system that makes the processing solution containing a color developing agent unnecessary, the Pictrography system is provided by Fuji Photo Film Co., Ltd. In this system, a small amount of water is supplied to a photographic element containing a base precursor, the resulting photographic element is brought into face-to-face contact with an image-receiving element, and then heat is applied thereto to cause the development reaction. Since such a system has the environmental advantage of using no processing baths, the thought which occurs first is to utilize it for the image formation in photosensitive materials for taking photographs.
As an example thereof, the method of incorporating a developing agent and couplers in a photosensitive material to form developed color images therein is disclosed in JP-A-9-10506 (the term "JP-A" as used herein means an "unexamined published Japanese patent application) and European Patent 0,762,201.
The Pictrography system makes the use of a developing solution unnecessary, and therein the mere supply of a small amount of water can trigger off the development. In other words, the base generation necessary for the progress of heat development is effected by the foregoing simple method. Further, the system of the foregoing type, or the system of incorporating a developing agent together with couplers in a photosensitive material and promoting the development by heating, is known to have an advantage of enabling a sharp reduction in development-processing time, specifically a reduction to from 1/5 to 1/20 of conventional ones.
It has so far been said that the method of causing the coupling reaction by generation of a base from the developing agent incorporated in a photosensitive material, supply of a base from the outside, or/and heating is effective in realizing the simple and rapid processing which is the trend of the times. And various attempts have been made.
Although the developing method comprising the incorporation of a developing agent in a photosensitive material and a heating operation is useful in particular, it has a big problem of tending to cause fog generation. In the case of such a developing method, it has further been revealed that the nondiffusible hydroquinones generally used as color stain inhibitor in conventional silver halide color photographic materials were practically ineffective for inhibiting the generation of color stains at the time of processing, but on the contrary they greatly aggravated the processing fog. Furthermore, the incorporation of both developing agent and photographically useful group (PUG) releasing coupler in a photosensitive material has been shown to have a great problem of causing the generation of serious fog and the lowering of sensitivity.
Thus, the development of techniques for preventing color stains from generating at the time of processing while desirably controlling the image structure by the use of PUG releasing compounds has become an urgent task.